Below are some of my most impressive blunders from classical games. In the first game, after defending well with black for 30+ moves, I blundered it all away with a careless bishop move.

Below is another pretty amazing mistake, although this one was in mutual time trouble and white also missed various chances to win. Still, missing mate in two (three if you count the white queen move) is pretty bad.

Fortunately I sometimes also play good games, and do not miss such opportunities when I get them. The recent game below shows others make mistakes too!